The invention relates to a blade holder for cutting machines with a blade head, which is supported at a lowering device, and with an advancing device for the circular blade secured at the blade head, whereby the advancing device, for movement of the circular blade between a cutting position and a ready position comprises a compressed-air actuated advancing piston rod with an advancing piston guided in a chamber of the housing of the blade head whereby the advancing piston rod is pretensioned by a pressure spring into the ready position of the circular blade.
A blade holder with the aforementioned features is disclosed in DE 41 14 059 A1. The blade head which supports the circular blade is positioned at the end of a lowering piston rod with which the circular blade is lowered into the cutting plane and, respectively, lifted therefrom. The advancing device arranged within the blade head provides for an adjustment of the circular blade transverse to the axis of the lowering piston into a contact position at a lower blade and, respectively, lifts the circular blade away from the lower blade when no cutting action is performed.
For performing these movements, the advancing device comprises an advancing piston which is actuated by compressed air in the direction of the cutting position of the circular blade, while, for return of the circular blade from the cutting position, a pressure spring is provided that loads the advancing piston rod into the ready position for the circular blade. Accordingly, the cutting force between the circular blade and the corresponding lower blade is predetermined and, respectively, adjustable by the pressing force in the direction of the cutting position of the circular blade provided by the pneumatically activated advancing piston which overcomes the effect of the pretensioned pressure spring.
Such a design of the blade holder has the disadvantage that the aforementioned kind of cutting force control is not sufficiently precise because of the employed pressure spring having own in tolerances and non-constant spring characteristic lines. When in the frame of such a cutting machine a plurality of such blade holders is used, a pneumatic drive pressure adjusted identically for each blade holder and the advancing piston does not accordingly produce an identical cutting force because, as a function of the respectively lifting position of the circular blade, respectively, of the lifting piston rod and as a function of the spring tolerances and the spring characteristic line of the respective pressure spring, a spring force of a different magnitude counteracts the pneumatic drive pressure acting in the direction of the cutting position of the circular blade.
From DE 26 57 792 A1 a blade holder is known in which by eliminating a pressure spring for returning the advancing piston rod into its ready position, the movement of the advancing position rod into the cutting position as well as into the ready position is realized by a pneumatic system. Such an embodiment, however, is complicated with respect to controlling the respective pneumatic drive for the two movement directions.
It is an object of the invention to improve for a blade holder of the aforementioned kind, including a pressure spring for effecting the return of the advancing piston rod, the precision of the cutting force control.